Semiconductor structure having low thermal stress and method for manufacturing thereof

ABSTRACT

A semiconductor structure includes a Si substrate, a supporting layer and a blocking layer formed on the substrate and an epitaxy layer formed on the supporting layer. The supporting layer defines a plurality of grooves therein to receive the blocking layer. The epitaxy layer is grown from the supporting layer. A plurality of slots is defined in the epitaxy layer and over the blocking layer. The epitaxy layer includes an N-type semiconductor layer, a light-emitting layer and a P-type semiconductor layer. A method for manufacturing the semiconductor structure is also disclosed.

BACKGROUND

1. Technical Field

The present disclosure relates to a semiconductor structure and a method for manufacturing thereof, and more particularly, to a semiconductor structure having low thermal stress and a method for manufacturing thereof.

2. Description of Related Art

As new type light source, LEDs are widely used in various applications. An LED often includes an LED chip to emit light. A conventional LED chip includes a substrate, an N-type semiconductor layer, a light-emitting layer and a P-type semiconductor layer sequentially grown on the substrate. The substrate is generally made of sapphire (Al₂O₃) for providing growing environment to the layers. However, such sapphire substrate has a low heat conductive capability, causing that heat generated by the layers cannot be timely dissipated. Therefore, a new type substrate made of Si is developed. Such Si substrate has a heat conductive index larger than the sapphire substrate so that the heat generated by the layers can be effectively removed.

Nevertheless, the coefficient of thermal expansion (CTE) of the Si substrate does not well match with that of the layers. Thus, during operation of the LED chip, the Si substrate has a deformation different from that of the layers, resulting in a thermal stress concentrated at an interface between the substrate and the layers. Such concentrated thermal stress may cause fracture of the layers or even damage of the LED chip.

What is needed, therefore, is a semiconductor structure which can overcome the limitations described above.

BRIEF DESCRIPTION OF THE DRAWINGS

Many aspects of the present disclosure can be better understood with reference to the following drawings. The components in the drawings are not necessarily drawn to scale, the emphasis instead being placed upon clearly illustrating the principles of the present disclosure. Moreover, in the drawings, like reference numerals designate corresponding parts throughout the several views.

FIG. 1 shows a first process of manufacturing a semiconductor structure of a first embodiment of the present disclosure.

FIG. 2 shows a second process of manufacturing the semiconductor structure of the first embodiment of the present disclosure.

FIG. 3 shows a third process of manufacturing the semiconductor structure of the first embodiment of the present disclosure.

FIG. 4 shows a forth process of manufacturing the semiconductor structure of the first embodiment of the present disclosure.

FIG. 5 shows a fifth process of manufacturing the semiconductor structure of the first embodiment of the present disclosure.

FIG. 6 shows the semiconductor structure of the first embodiment which has been manufactured after the processes of FIGS. 1-5.

FIG. 7 shows a semiconductor structure of a second embodiment which has been manufactured after the processes of FIGS. 1-5.

DETAILED DESCRIPTION OF THE EMBODIMENTS

Referring to FIG. 6, the present disclosure discloses a semiconductor structure which has a low thermal stress. The semiconductor structure includes a substrate 100, a supporting layer 101 a and a blocking layer 103 alternately formed on a top face of the substrate 100 and an epitaxy layer 104 formed on the supporting layer 101 a.

The substrate 100 may be made of sapphire, Si, SiC or GaN, wherein Si is preferable in the present disclosure. The material of Si has a heat conductive index larger than that of sapphire so that the substrate 100 can have a better heat conduction capability. The supporting layer 101 a may be an AlN or Al₂O₃ layer. The supporting layer 101 a is divided by multiple grooves 105 to form a plurality of spaced islands. The blocking layer 103 is discontinuously distributed in the grooves 105 to be alternate with the islands of the supporting layer 101 a. The blocking layer 103 may be a SiO₂ or Si₃N₄ layer which has a thickness far less than that of the blocking layer 101 a. Preferably, the thickness of the blocking layer 103 is about one-fifth (⅕) of that of the blocking layer 101 a. The epitaxy layer 104 includes an N-type semiconductor layer, a light-emitting layer and a P-type semiconductor layer (not shown) sequentially grown from a top face of the supporting layer 101 a. The N-type semiconductor layer may be an N-doped GaN, AlGaN, InGaN or AlInGaN layer, the P-type semiconductor layer may be a P-doped GaN, AlGaN, InGaN or AlInGaN layer, and the light-emitting layer may be a multi-quantum well structure. Since the blocking layer 103 prevents the epitaxy layer 104 from growing on a top surface thereof, the epitaxy layer 104 can only be grown on the top face of the supporting layer 101 a vertically and upwardly. During vertical growth, the epitaxy layer 104 also has a lateral growing trend so that discrete parts of the epitaxy layer 104 grown from the top face of the supporting layer 101 a would join with each other at places over the blocking layer 103. The epitaxy layer 104 is thus grown to a continuous layer. The epitaxy layer 104 forms a plurality of triangle slots 106 over the blocking layer 103 and communicating with the grooves 105, respectively. Each of the slots 106 has a width gradually decreasing along a direction from the substrate 100 towards the epitaxy layer 104.

Also referring to FIGS. 1-5, a method for manufacturing the above semiconductor structure is given below, including steps:

1) providing a Si substrate 100;

2) forming an aluminum film 101 on the substrate 100, the aluminum film 101 can be formed on the substrate 101 by thermal evaporation, E-beam evaporation, ion-beam sputtering, chemical vapor deposition, physical vapor deposition or electroplating;

3) forming a patterned photoresist layer 102 on the aluminum film 101, the photoresist layer 102 being patterned by lithography to form multiple gapped areas, in which the shapes of the areas can be selected from circle, rectangle, triangle or other suitable shapes, depending on actual requirements;

4) etching the aluminum film 101, wherein since parts of the aluminum film 101 just below the gapped areas of the photoresist layer 102 are protected by the photoresist layer 102, they would not be etched and continue remaining on the top face of the substrate 100; while the other parts of the aluminum film 101 exposed under gaps between the areas of the photoresist layer 102 would be fully etched to expose the top face of the substrate 100;

5) removing the photoresist layer 102 by etching or other methods to expose the remaining aluminum film 101;

6) putting the substrate 100 into a high-temperature environment containing plenty of O₂ or N₂, in which the aluminum film 101 on the substrate 100 is oxidized or nitrided to Al₂O₃ or AlN to thereby form a supporting layer 101 a, and the exposed top face of the Si substrate 100 is oxidized or nitrided to SiO₂ or Si₃N₄ to thereby form a blocking layer 103; and

7) growing an epitaxy layer 104 on the supporting layer 101 a.

The temperature of the environment in step 5) can be controlled according to the thickness of the aluminum film 101 and reaction time of the aluminum film 101 and the substrate 100; however, a temperature higher than 1000 is preferable in the present disclosure.

Also referring to FIG. 7, by controlling relation between a width D of each groove 105 and a thickness d of the epitaxy layer 104, the lateral growing of the epitaxy layer 104 can be limited to leave the slots 106 a extending through the whole epitaxy layer 104. The epitaxy layer 104 is thus divided by the slots 106 a to plural of individual islands. Preferably, the width D of each groove 105 and the thickness d of the epitaxy layer 104 should conform to the relation of D>2d, to realize the separation between the islands of the epitaxy layer 104. Such discrete islands of the epitaxy layer 104 can be directly used as LED chips without further dicing, thereby reducing manufacturing process of the semiconductor structure.

Furthermore, a buffer layer (not shown) can be formed on the top face of the supporting layer 101 a before growing the epitaxy layer 104. The buffer layer can provide better growing environment for the epitaxy layer 104 so that less dislocations would be generated within the epitaxy layer 104. The buffer layer can be made of GaN, AlN or other suitable materials.

The grooves 105 between bottom areas of the epitaxy layer 104 can effectively relieve concentrated thermal stress between the epitaxy layer 104 and the substrate 100, thereby protecting the epitaxy layer 104 from facture. In addition, since difference of the refractive index between the epitaxy layer 104 and air contained within the slots 106, lateral faces of the epitaxy layer 104 defining the slots 106 can totally reflect more light emitted downwardly from the epitaxy layer 104 towards a top face of the epitaxy layer 104, thereby increasing light-extracting efficiency of the semiconductor structure.

It is believed that the present disclosure and its advantages will be understood from the foregoing description, and it will be apparent that various changes may be made thereto without departing from the spirit and scope of the present disclosure or sacrificing all of its material advantages, the examples hereinbefore described merely being preferred or exemplary embodiments. 

What is claimed is:
 1. A method for manufacturing a semiconductor structure, comprising steps of: 1) providing a Si substrate; 2) forming an aluminum film on the substrate; 3) patterning the aluminum film to form a plurality of grooves in the aluminum film, a top face of the substrate being exposed within the grooves; 4) putting the substrate in an environment filled with reaction gas, the aluminum film being reacted to form a supporting layer, and the top face of the substrate exposed in the grooves being reacted to form a blocking layer; and 5) growing an epitaxy layer on the supporting layer, wherein the blocking layer prevents the epitaxy layer from growing therefrom to form a plurality of slots in a bottom face of the epitaxy layer.
 2. The method as claimed in claim 1, wherein the blocking layer has a thickness less than that of the supporting layer.
 3. The method as claimed in claim 1, wherein the slots communicate with the grooves, respectively.
 4. The method as claimed in claim 1, wherein the slots are terminated into an interior of the epitaxy layer.
 5. The method as claimed in claim 1, wherein the slots are extended through the epitaxy layer to divide the epitaxy layer into a plurality of individual parts.
 6. The method as claimed in claim 1, wherein patterning the aluminum film is implemented by forming a photoresist layer on the aluminum film, and then defining the photoresist layer into multiple areas which are spaced from each other by gaps, etching the aluminum film exposed within the gaps as a desired pattern, and finally removing the photoresist layer from the aluminum film.
 7. The method as claimed in claim 1, wherein a width of each of the grooves is twice larger than a thickness of the epitaxy layer.
 8. The method as claimed in claim 1, wherein the reaction gas in step 4) is O₂ or N₂, and the aluminum film is reacted to Al₂O₃ or AlN and the top face of the substrate is reacted to SiO₂ or Si₃N₄. 